Progress came after Aylesbury - in which nearly all prisoners are serving sentences from four years to life - was placed in prison service 'special measures', with its population halved to 200.

Peter Clarke, HM Chief Inspector of Prisons, expressed serious concern about the potential impact for the treatment and conditions of Aylesbury prisoners if the population were to be increased without additional staff.

In April 2017, safety was assessed as poor while other healthy prison assessments were not sufficiently good. In 2019, safety had risen one grade and in all the tests outcomes were now not sufficiently good.

However, Mr Clarke added:

"It would be quite wrong to infer that there had been no progress made in the time since the last inspection.

"What we found was that there had been some distinct movement and indeed some improvements within the gradings."

The overall rate of violence had increased, but the seriousness of most of it had declined, possibly a consequence of introducing some 'freeflow' (allowing prisoners to move about and potentially mix in parts of the prison).

"This has made it easier for prisoners to gain access to one another and fight, but at the same time more likely to be in the sight of officers who are able to intervene and de-escalate situations before they become very serious."

Inspectors have seen this phenomenon elsewhere.

The daily regime had been inadequate at Aylesbury for many years, and it remained the case that, for much of the week, there was no evening association, time out of cell was poor and often unpredictable and there was no opportunity at all for prisoners to eat together.

Mr Clarke commented:

"For these very basic socialisation processes to be absent or poor in a prison holding young adults was clearly unacceptable and needed to be addressed.

"The fact that the population had halved while staff levels had remained the same should have enabled more positive changes to have been made."

HM Inspectorate of Prisons has frequently reported that the nationally mandated process for assessing the risks presented by, and the needs of, prisoners (OASys) is "showing worrying signs of systemic failure, in some places verging on collapse."

At Aylesbury in 2017, inspectors made a main recommendation that concerted action should be taken to reduce the OASys backlog but, Mr Clarke said, in 2019

"inexplicably, considering the risks presented by the population at Aylesbury, this had not been acted upon. We found that over a quarter of the prisoners did not have an OASys at all, and too few of the remainder had received proper or timely reviews."

Overall, Mr Clarke said:

"It was clear that Aylesbury was an institution in transition. It was reassuring that in this instance I was able to see some positive impact from the prison being in 'special measures'. The halving of the roll, closure of wings pending refurbishment and attempts to relax the regime had had a positive impact.

"It was easy for me to see a real sense of ownership and teamwork in support of the measures that were being taken to improve performance.

"However, I was concerned by suggestions that there might be plans to return the roll to its previous number of around 400, but without increasing staff numbers. If this were to happen - and I hope it does not, at least in the short term - I would be very worried about the potential impact on the treatment of and conditions experienced by the prisoners.

"There were some positive signs of progress at Aylesbury, an establishment that has experienced some very challenging times. It would be a pity if that progress were to be put in jeopardy."